The present invention relates to a modulating method for generating a signal modulated by orthogonal frequency division multiplexing (to be referred to as xe2x80x98OFDMxe2x80x99 hereinafter), a modulator utilizing the modulation method, a demodulating method for demodulating the OFDM-modulated signal and a demodulator utilizing the demodulation method. The present invention relates to, in particular, a technique suited for processing an interleaved OFDM modulation signal.
Conventionally, OFDM modulation has been put to practical use as one of modulation systems in case of radio-transmitting relatively mass storage digital data. As shown in, for example, FIG. 23, in a relatively small space such as a home or an office floor, a picture signal (digital picture data) outputted from a picture signal source 1 consisting of a tuner receiving television broadcasting, a reproducing apparatus for reproducing a picture program recorded in a recording medium and the like is supplied to a radio transmitter 2. The picture signal is modulated to an OFDM modulated signal at a radio transmitter 2 and the modulated signal is radio-transmitted from an antenna 3 in a predetermined frequency band. The radio-transmitted signal is received by a radio receiver 5 connected to an antenna 4. The received OFDM wave in the frequency band is demodulated and a picture signal is thereby obtained. The received picture signal is supplied to a video recording and reproducing apparatus 6, in which the signal is recorded in a predetermined recording medium such as a video tape, or supplied to an image receiving machine 7 and subjected to image receiving process. In this case, it is possible to reproduce the picture signal recorded in the video recording and reproducing apparatus 6 and to supply the resultant reproduced signal to the image receiving machine 7 to thereby allow an image to be received by the image receiving machine 7.
With this system arrangement, it is possible to highly efficiently radio-transmit mass storage digital data by using the OFDM modulated signal for radio transmission between the antenna 3 connected to the radio transmitter 2 and the antenna 4 connected to the radio receiver 5.
Now, with reference to FIG. 24 showing an example of the constitution of the radio transmitter 2 for conducting OFDM modulation for transmission, a transmission signal (digital data) obtained at an input terminal 2a is supplied to a serial/parallel converter 2b and converted to parallel data for each predetermined unit. The parallel data converted at the serial/parallel converter 2b is supplied to an interleave memory 2c in which interleave processing for changing write and read orders for writing and reading data to/from the memory 2c and changing data array. The interleaved parallel data is supplied to an inverse Fourier transform circuit (or IFFT circuit) 2d, in which time axis data is orthogonally transformed to frequency axis data by arithmetic operation by means of inverse fast Fourier transform. The orthogonally transformed parallel data is supplied to a parallel/serial converter 2e and converted to serial data, which serial data is supplied to an output terminal 2f. The data obtained at the output terminal 2f is supplied to a transmission processing system to convert the frequency to fall within the range of a predetermined transmission frequency band, thereafter radio-transmitting the data.
Next, with reference to FIG. 25 showing an example of a constitution in which the signal thus radio-transmitted is received and demodulated by the radio receiver 5, a signal in a predetermined frequency band is received and a signal frequency-converted to an intermediate frequency signal is obtained at the input terminal 5a. The data obtained at the input terminal 5a is supplied to a serial/parallel converter 5b and converted to parallel data for each predetermined unit. The converted output is supplied to a Fourier transform circuit (FFT circuit) 5c, in which orthogonal transform processing for transforming frequency axis data to time axis data by arithmetic operation by means of fast Fourier transform. The orthogonally transformed parallel data is supplied to a de-interleave memory 5d, in which de-interleave processing for changing write and read orders for writing and reading data to/from the memory 5d, changing data array back to an original data array is conducted. The de-interleaved parallel data is supplied to the parallel/serial converter 5e and converted to serial data, which serial data is supplied to the output terminal 5f. 
The demodulation processing for demodulating the OFDM modulation signal conducted with the constitution shown in FIG. 25 is executed at timing shown in FIG. 26. That is to say, there are, first, a data input time Ta at which data is inputted to the Fourier transform circuit 5c, next a Fourier transform processing time Tb at which Fast Fourier transform is conducted at the Fourier transform circuit 5c and then a data output time Tc at which the Fourier-transformed data is outputted. The data outputted at the output time Tc is simultaneously written in the de-interleave memory 5d and the data written in the memory 5d is read at a read-out time Td. It is noted that transform processing for generating an OFDM modulation signal with the constitution of FIG. 24 is basically opposite to the demodulation processing and requires the same time as that for the demodulation processing.
Now, description will be given to a case where data is interleaved and transmitted by the transmission processings of FIGS. 24 and 25, with reference to FIGS. 27 and 28. As shown in FIG. 27A, for example, if OFDM modulation for distributing data in 50 units of data numbers of k=0 to 49 to sub-carriers x0 to x50 and transmitting them is conducted and this signal is correctly received by a receiver side, then no problem occurs. On the other hand, as shown in FIG. 27B, for example, it is assumed that sub-carriers of data numbers k=5, 6 and 7 cannot be correctly received due to multi-pass fading or the like and that the items of data numbered k=5, 6 and 7 are lost.
At this time, if data is transmitted without interleave processing, data items of three consecutive units in one slot, i.e., k=5, 6 and 7 are lost, resulting in burst error as shown in FIG. 28A. If such a burst error occurs, it is difficult to completely restore data using an error correction code. If data is transmitted after interleave processing, by contrast, data items of three units of k=5, 6 and 7 are arranged in a distributed manner in one slot (the distribution state varies according to interleave conditions) as shown in, for example, FIG. 28B. Then, a possible error becomes random errors, each of which can be completely corrected by using error correction codes or the like.
By transmitting data after subjecting the data to interleave processing, it is possible to minimize data loss at the receiver side and to ensure a good transmission condition.
Meanwhile, with the constitution shown in FIG. 25, interleave processing is conducted using a memory. There is also proposed a constitution in which de-interleave processing is conducted without using a memory. FIG. 29 shows an example of the latter case. Processing steps shown therein are the same until data obtained at an input terminal 5a is supplied to a serial/parallel converter 5b and converted to parallel data for each predetermined unit, and the conversion output is supplied to a Fourier transform circuit 5c, in which orthogonal transform for transforming frequency axis data to time axis data is conducted by arithmetic operation by means of Fast Fourier transform. The orthogonally transformed parallel data is subjected to processing for changing a data array by wiring change processing 5d corresponding to the interleave pattern of the data. The parallel data which data array has been thus changed is supplied to a parallel/serial converter 5e and converted to serial data. The serial data is then supplied to an output terminal 5f. 
The demodulation processing for demodulating an OFDM modulation signal conducted with the constitution shown in FIG. 29 is executed at timing shown in FIG. 30. That is to say, there are, first, a data input time Te at which data is inputted to the Fourier transform circuit 5c, next a Fourier transform processing time Tf at which fast Fourier transform is conducted at the Fourier transform circuit 5c, and then an output time Tg at which the data thus Fourier-transformed is outputted. With this constitution, the data is outputted from the Fourier transform circuit 5c and supplied to the parallel/serial converter 5e and, at the same time, de-interleaved by wiring change processing.
If a convolutionally coded signal is modulated to an OFDM modulation signal, thinning-out processing called puncture, processing is sometimes conducted. FIG. 31 shows an example of a conventional constitution with which this puncture processing is conducted. Transmission data ai obtained at an input terminal 8a is convolutionally coded by a convolutional coder 8b and two sets of data G1 and G2 are generated. The two data sets G1 and G2 are supplied to a thinning-out processing circuit 8c and thinned out, and coded data bi which has been subjected to puncture processing is thereby obtained. Here, it is assumed that if the coding rate of the convolutional coder 8b is r=xc2xd, a coding rate at which the puncture-processed data bi is coded is r={fraction (3/4)}. An example of the constitution of the convolutional coder with a coding rate of r=xc2xd is shown in FIG. 33. In FIG. 33, transmission data ai obtained at the input terminal 9a is supplied to a shift register 9b. The shift register 9b consists of three stages, in which data stored in the first stage and that in the third stage are supplied to and added together by an adder 9c and data G1 is thereby obtained and in which data stored in the first stage and that in the second stage are supplied to and added together by an adder 9d and data G2 is thereby obtained.
The thinning-out processing state of the two data sets of G1 and G2 thus convolutionally coded is shown in FIG. 33. If a data sequence of a0, a1, a2 . . . shown in, for example, FIG. 33A forms input data ai, two data sets G1 and G2 which have been convolutionally coded become data g10, g11, g12, . . . and data g20, g21, g22, . . . as shown in FIGS. 33B and 33C, respectively. At a thinning-out processing circuit 8c, using, for example, data g10, g11, g12, g20, g21 and g22, the data are outputted in the order of g10, g20, g21, and g12 as shown in FIG. 33D. Namely, as indicated by x marks shown in FIGS. 33B and 33C, data g11 and g22 are thinned out. The data bi thus thinned out eventually becomes data convolutionally coded at a coding rate of r={fraction (3/4)}.
In modulation processing for modulating an OFDM modulation signal, if interleave processing is conducted using a memory as shown in FIG. 24, a modulation processing constitution is disadvantageously complicated because of the need of the memory. Also, the modulation processing time is disadvantageously longer than that for a case where data which is not interleaved is processed by the time required for reading data from the interleave memory.
Further, if puncture processing using the convolutional coder shown in FIG. 31 is conducted during modulation, the constitution for puncture processing is disadvantageously complicated. That is, as can be seen from FIG. 33 showing a puncture processing state, the clock rate of input data (FIG. 33A) is not an integral multiple of that of puncture-processed output data (FIG. 33B). A clock of two-thirds of a data clock is required for thinning-out processing and the generation of such clocks tends to make constitution complex. Besides, it also requires processing for re-timing the thinned-out data, which makes a relevant circuit larger in size and it requires high power consumption. In addition, since clocks with different frequencies are used, spurious radiation occurs and it adversely affects a high frequency circuit block in which modulation signals are radio-transmitted or received. The adverse influences involve, for example, the deterioration of reception characteristics and the occurrence of emission interference of the out-side spurious wave.
Moreover, in case of demodulating an OFDM modulation signal and conducting de-interleave processing using a memory as shown in FIG. 25, the demodulation processing constitution is disadvantageously complicated because of the need of the memory. As for demodulation processing time, the processing time T1 shown in FIG. 26 includes longer demodulation processing time than that in a case of processing data which is not interleaved, by the time required for reading data from the de-interleave memory. Thus, demodulation processing disadvantageously is lengthened.
As shown in FIG. 29, if de-interleave processing is conducted at processing for changing the wiring of parallel data outputted from the Fourier transform circuit, a processing time T2 shown in FIG. 30 is the same as that for dealing with data which is not interleaved, in which case the problem of lengthened processing time does not occur. Still, due to the need to provide a parallel/serial converter 5e at the output part, a circuit board in which a demodulator circuit for OFDM modulation signals is incorporated is disadvantageously made larger in size.
It is the first object of the present invention to make it possible to realize modulation processing for generating an interleaved OFDM modulation signal with a simple constitution at a short processing time.
It is the second object of the present invention to make it possible to realize processing for demodulating an interleaved OFDM modulation signal with simple constitution in a short processing time.
The first invention is a modulation method characterized by comprising the steps of retaining predetermined data as N sets of data, where N is an arbitrary integer; and sequentially outputting the retained N data sets in an order indicated by predetermined output order data and transforming the outputted N data to data arranged on a frequency axis in a distributed manner at predetermined frequency intervals. This makes it possible to interleave the data in an order in which the data are supplied to conduct inverse Fourier transform and to simplify processing for interleave processing. In addition, it take no time to conduct interleave processing. Thus, time required for transform processing can be reduced.
The second present invention according to the first invention, i.e., the modulation method, is characterized in that the output order data is generated by count processing. This makes it possible to easily generate signal order data by count processing and to conduct interleave processing.
The third invention according to the first invention, i.e., the modulation method, is characterized in that the output order data causes data prepared in advance to be sequentially outputted. This makes it possible to conduct interleave processing by simple processing for preparing output order data in advance.
The fourth invention according to the first invention, i.e., the modulation method, is characterized by comprising the steps of delaying one set of data out of the two sets of data generated by convolutional coding by a one-clock time of the data; and sequentially outputting the delayed set of data and undelayed set of data in the order indicated by the predetermined output order data, and transforming the outputted data to data arranged on the frequency axis in a distributed manner at predetermined frequency intervals. This makes it possible to efficiently interleave convolutionally coded data to an OFDM modulation signal by simple processing.
The fifth invention according to the first invention, i.e., the modulation method, is characterized by comprising the step of parallel processing data of Q-bit words as processing for transforming the data of Q-bit words to the data arranged on the frequency axis in a distributed manner at the predetermined frequency intervals, where Q is an integer equal to or higher than 2. This makes it possible to efficiently process data in units of words consisting of a plurality of bits.
The sixth invention is a modulation method characterized by comprising the steps of generating first interleaved data and second interleaved data from predetermined data; and while simultaneously using the first and second interleaved data, transforming the first and second interleaved data to data arranged on a frequency axis in a distributed manner at predetermined frequency intervals. This makes it possible to inversely Fourier-transform the interleaved data in a short time to thereby reduce modulation processing time.
The seventh invention according to the sixth invention, i.e., the modulation method, is characterized by comprising the steps of differentially coding the first and second interleaved data irrespectively of each other; and while simultaneously using the respective differentially coded data, transforming the differentially coded data to data arranged on the frequency axis in a distributed manner at predetermined frequency intervals. This makes it possible to efficiently conduct differential coding during interleave processing.
The eighth invention is a modulator characterized by comprising N registers to which predetermined data is simultaneously supplied, where N is an arbitrary integer; output order data generating means for generating data for designating an output order of the data supplied to the N registers; and inverse Fourier transform means for transforming the supplied N data to data arranged on a frequency axis in a distributed manner at predetermined frequency intervals in the order designated by the output order data generating means. This makes it possible to interleave data at the time the data is inputted to the inverse Fourier transform means. As a result, there is no need to provide a large circuit such as a memory for interleave processing and the interleave processing is conducted simultaneously with input selection. Thus, modulation processing time is not lengthened since interleave processing time is not added to the modulation processing time.
The ninth invention according to the eighth invention, i.e., the modulator, is characterized in that a counter sequentially generating data corresponding to the output order by means of count processing is employed as the output order data generating means. Thus, by generating the output order data by the count processing of the counter, it is possible to easily generate signal order data using the counter and to conduct interleave processing.
The tenth invention according to the eighth invention, i.e., the modulator, is characterized in that a shift register sequentially outputting data prepared in advance is employed as the output order data generating means. This makes it possible to conduct interleave processing with simple constitution in which the shift register is employed.
The eleventh invention according to the eighth invention, i.e., the modulator, is characterized by comprising: convolutional coding means; delay means for delaying one set of data out of two sets of data coded by the convolutional coding means by a one-clock time of the data; and hold means for temporarily holding the output order data outputted by the output order data generating means, and characterized in that one set of data delayed by the delay means and the other set of data outputted by the convolutional coding means are supplied to the register. This makes it possible to efficiently interleave the convolutionally coded data to an OFDM modulation signal with simple constitution.
The twelfth invention according to the eighth invention, i.e., the modulator, is characterized in that the inverse Fourier transform means parallel-processes data of Q-bit words, where Q is an integer equal to or higher than 2. This makes it possible to efficiently process data in units of words consisting of plural bits with simple constitution.
The 13th invention is a modulator characterized by comprising first and second interleave means for interleaving predetermined data; and inverse Fourier transform means for inputting data outputted from the first and second interleave means to different points and transforming the outputted data to data arranged on a frequency axis in a distributed manner at predetermined frequency intervals. This makes it possible to input the interleaved data to the inverse Fourier transform means and process them in a short time.
The 14th invention according to the 13th invention, i.e., the modulator, is characterized by comprising first differential coding means for differentially coding an output of the first interleave means; and second differential coding means for differentially coding an output of the second interleave means, and characterized in that coded outputs of the first and second differential coding means are supplied to the inverse Fourier transform means. Thus, it is possible to differentially code and inversely Fourier-transform the interleaved data efficiently.
The 15th invention is a demodulation method characterized by comprising the steps of transforming data arranged on a frequency axis in a distributed manner at predetermined frequency intervals to N points of data for every predetermined unit; and selecting and outputting points of data designated by predetermined output order data from the transformed N points of data. This makes it possible to conduct de-interleave processing during processing for selecting data to be outputted from the Fourier-transformed data. Thus, processing for de-interleave processing is simplified and does not require any additional time, whereby time required for demodulation processing can be reduced.
The 16th invention according to the 15th invention, i.e., the demodulation method, is characterized in that the output order data is sequentially generated by count processing. This makes it possible to easily generate signal order data by count processing and to conduct de-interleave processing.
The 17th invention according to the 15th invention, i.e., the demodulation method, is characterized in that the output order data causes data prepared in advance to be sequentially outputted. This makes it possible to conduct de-interleave processing by simple processing for preparing output order data in advance.
The 18th invention according to the 15th invention, i.e., the demodulation method, is characterized by comprising the step of dividing the transformed N points of data to two sets of data, and selecting and outputting points from the two sets of data based on the output order data irrespectively of each other. This makes it possible to simultaneously obtain plural sets of demodulation data.
The 19th invention according to the 18th invention, i.e., the demodulation method, is characterized by comprising the step of conducting differential demodulation using the two sets of data which points are selected and outputted irrespectively of each other. This makes it possible to easily conduct good differential demodulation processing.
The 20th invention according to 19th invention, i.e., the demodulation method, is characterized by comprising the step of delaying one set of data out of the two sets of data, which points are selected and outputted respectively, by a predetermined time. This makes it possible to conduct appropriate selection processing.
The 21st invention according to the 18th invention, i.e., the demodulation method, is characterized by comprising the step of conducting Viterbi decoding using the two sets of data which points are selected and outputted irrespectively of each other. This makes it possible to conduct good Viterbi decoding.
The 22nd invention according to 15th invention, i.e., the demodulation method, is characterized by comprising the steps of dividing the transformed N points of data to four sets of data and individually selecting and outputting points from the four sets of data based on the output order data; conducting differentially demodulation using selected first set of data and second set of data; conducting differentially demodulation using selected third set of data and fourth set of data; and conducting Viterbi decoding using the respective differentially demodulated data. This makes it possible to conduct differential demodulation using Fourier-transformed N points of data and conduct Viterbi decoding using the differentially demodulated data. Thus, good demodulation data can be obtained as a result of differential demodulation and Viterbi decoding.
The 23rd invention according to 22nd invention, i.e., the demodulation method, is characterized by comprising the steps of preparing first and second output order data as the output order data; selecting the first set of data based on the first output order data; selecting the second set of data based on data delayed by a predetermined time from the first output order data; selecting the third set of data based on the second output order data; and selecting the fourth set of data based on data delayed by a predetermined time from the second output order data. Thus, by generating two output order data, it is possible to individually select points using four sets of data and to thereby conduct good processing using only two output order data.
The 24th invention according to the 22nd invention, i.e., demodulation method, is characterized by comprising the step of designating selected points of the four sets of data based on the output order data respectively generated. This makes it possible to conduct appropriate processing for every set of data.
The 25th invention according to the 22nd invention, i.e., demodulation method, is characterized by comprising the steps of selecting the third set of data based on predetermined output order data; selecting the fourth set of data based on data delayed by a predetermined time from the predetermined output order data; selecting the first set of data based on data obtained by adding a predetermined value to the predetermined output order data; and selecting the second set of data based on data delayed by a predetermined time from the data obtained by adding the predetermined value to the predetermined output order data. Thus, by processing one output order data to provide data for selecting four sets of data, it is possible to conduct Viterbi decoding based on the two differentially demodulated data with simple constitution.
The 26th invention is a demodulator characterized by comprising Fourier transform means for transforming data arranged on a frequency axis in a distributed manner at predetermined frequency intervals to N points of data for every unit, where N is an arbitrary integer; selecting means for selecting and outputting designated points of data from the N points of data outputted by the Fourier transform means; and output order data generating means for generating data for designating points selected by the selecting means. Thus, de-interleave processing is conducted while selecting data to be outputted from the Fourier-transformed data using selecting means. As a result, there is no need to provide a memory storing Fourier-transformed data or the like and a large circuit such as an output parallel/serial converter. Besides, since de-interleave processing is conducted simultaneously with the selection of outputted data, demodulation processing is not lengthened since it is not necessary to add time for conducting de-interleave processing to the demodulation processing.
The 27th invention according to the 26th invention, i.e., the demodulator, is characterized in that a counter sequentially generating data corresponding to an output order by means of count processing is employed as the output order data generating means. This makes it possible to conduct appropriate de-interleave processing with simple constitution in which a counter is used.
The 28th invention according to the 26th invention, i.e., the demodulator, is characterized in that a shift register sequentially outputting data prepared in advance is employed as the output order data generating means. This makes it possible to conduct appropriate de-interleave processing with simple constitution in which a shift register is used.
The 29th invention according to the 26th invention, i.e., the demodulator, is characterized in that the N points of data outputted by the Fourier transform means are supplied to first and second selecting means to cause the first and second selecting means to individually select and output points based on an output of the output order data generating means. This facilitates simultaneously obtaining plural sets of demodulation data.
The 30th invention according to the 29th invention, i.e., the demodulator, is characterized by comprising differential demodulation means, to which the points of data selected by the first selecting means and the points of data selected by the second selecting means are supplied, for conducting differential demodulation using the two sets of data. This makes it possible to conduct good differential demodulation processing with simple constitution.
The 31st invention according to the 30th invention, i.e., the demodulator, is characterized in that an output of the output order data generating means is directly supplied to the first selecting means and to the second selecting means through delay means for delaying the output of the output order data generating means by a predetermined time. This makes it possible to conduct appropriate selection processing using two selection means with simple constitution in which only one output order data generating means is used.
The 32nd invention according to the 29th invention, i.e., the demodulator, is characterized by comprising Viterbi decoding means, to which the points of data selected by the first selecting means and the points of data selected by the second selecting means are supplied, for conducting Viterbi decoding using the two sets of data. This makes it possible to conduct good Viterbi decoding using plural sets of demodulation data obtained with simple constitution.
The 33rd invention according to the 26th invention, i.e., the demodulator, is characterized in that the N points of data outputted by the Fourier transform means are supplied to first, second, third and fourth selecting means, and the selecting means individually select points based on an output of the output order data generating means; points of data selected by the first and second selecting means are supplied to and differentially demodulated by a first differential demodulation means; points of data selected by the third and fourth selecting means are supplied to and differentially demodulated by second differential demodulation means; and the data differentially demodulated by the first and second differential demodulating means are supplied to and Viterbi decoded by Viterbi decoding means. This makes it possible to conduct good Viterbi decoding based on the two differentially demodulated data.
The 34th invention according to the 33rd invention, i.e., the demodulator, is characterized in that the demodulator comprises first and second output order data generating means as the output order data generating means; and an output of the first output order data generating means is directly supplied to the first selecting means and supplied to the second selecting means through delay means for delaying the output of the first output order data generating means by a predetermined time, and an output of the second output order data generating means is directly supplied to the third selecting means and supplied to the fourth selecting means through delay means for delaying the output of the second output order data generating means by a predetermined time. This makes it possible to individually select points of data using four selecting means with simple constitution.
The 35th invention according to the 33rd invention, i.e., the demodulator, is characterized in that data for designating the points selected by the first, second, third and fourth selecting means are supplied from individual output order data generating means for the first, second, third and fourth selecting means respectively. This facilitates setting an optimal selection state for each selecting means.
The 36th invention according to the 33rd invention, i.e., the demodulator, is characterized in that an output of the output order data generating means is directly supplied to the third selecting means and supplied to the fourth selecting means through first delay means for delaying the output of the output order data generating means by a predetermined time, and an output of arithmetic operation means for adding a predetermined value to the output of the output order data generating means, is directly supplied to the first selecting means and supplied to the second selecting means through second delay means for delaying the output of the arithmetic operation means by a predetermined time. This makes it possible to conduct Viterbi decoding based on the two differentially demodulated date with simple constitution in which only one output order data generating means is used.